JPS5996217A - Manufacture of steel with superior sulfide cracking resistance - Google Patents

Abstract

PURPOSE:To improve the sulfide cracking resistance and yield strength of a steel contg. prescribed percentages of C, Si, Mn, P, S, Cr, Mo, Al and Ca by heat treating the steel under prescribed conditions. CONSTITUTION:A steel contg., by weight, 0.15-0.45% C, 0.05-0.8% Si, 0.3-1.7% Mn, <0.008% P, <=0.003% S, 0.2-1.5% Cr, 0.05-0.8% Mo, 0.01-0.1% Al and Ca satisfying Ca/S=1-10 is refined. The steel is rapidly heated to (the Ac3 point+30 deg.C) or above in a short time and quenched. The heat treatment is repeated once or more to make the austenite grains fine up to ASTM grain size No.10 or above. The steel is then tempered at the Ac1 point or below.

Description

[Detailed Description of the Invention] This invention has a high yield strength of 65 K7f/mrd or more, and exhibits excellent 11t sulfide cracking properties in a wet hydrogen sulfide environment, and is particularly suitable for use in oil and gas wells. The present invention relates to a method for manufacturing oil well steel suitable for use as mechanical structural members such as oil country tubular goods and line pipes, as well as equipment members used around oil and gas wells.

In recent years, in order to cope with the 2℃ energy situation, the development of 1i oil and gas fields has become active, and the development of 1i oil and gas fields has been actively carried out. Development efforts are now turning to oil and gas fields in so-called sour environments, where they are contaminated with somatic hydrogen (H2S). Therefore, in the field of oil and natural gas production in recent years, there is a need for deep wells. It has high strength and strong resistance to sulfide cracking, allowing it to withstand the pressure of vents and gases, as well as the tensile load caused by the hexagonal vehicle's own vehicle, and can fully demonstrate the desired performance even when used in sour environments. Demand for steel products is becoming stronger and stronger.

By the way, since around 1950, various companies have been conducting research on ways to increase the resistance of silver to sulfide cracking.
Based on the recognition that keeping the strength of the plow below the upper limit of hardness (strength) shown in R-01-75 (1977 Revision) is the most effective way to prevent sulfide cracking.

Based on this ([, -80J The lower limit of L yield strength is 800
00psi (5662K7f/mn?) J was added to the APIM rating to meet user requests.

However, as mentioned above, the world's energy situation is accelerating the development of acidic deep wells, and if low-strength YL products are used for oil country tubing for water wells, the required speed will inevitably increase to 14. i
＜As a result, there is a significant disadvantage in terms of economy and workability, so a steel material that is even stronger than rL-SC4 and has resistance to chemical cracking as well is required.
Especially these days.

The lower limit of yield strength is 9 (+ 000 psi (63,
There is also a growing demand for high-strength oil country tubular goods exceeding 3 to 9 f/mm").

Therefore, f+ for casing pipes has a higher hardness than rL −80J of the API standard! Various studies have been conducted on '4, and at first attention was focused on martensitic needle 1, which can achieve high strength relatively easily, but when used as a casing, it is often made of relatively thick material, Since the seamless pipe manufacturing method is used for manufacturing, it is extremely difficult to engrave from the inside of the pipe. It was impossible to completely avoid the formation of microstructures on the inner surface of the pipe.Also, this bainite structure does not bring good results to the corrosion resistance of copper, so the problem still remains that good corrosion resistance cannot be ensured in the end. It was something.

Therefore, in order to make effective use of B, we added 3 minutes of hardenability and also added Ti in order to make effective use of B.
However, in such high-strength steels, it has still not been possible to achieve a fully satisfactory corrosion resistance. In other words, to confirm monophagy,
The shell type test method shown in Figures 1 and 2 was developed as a result of extensive research comparing fruiting in numerous fields. ) is the formula, SC2(σy10゜75)XIO-' It is said that if you add all the grooves, no cracks will occur.
At high intensity ψR4, there was nothing to add δ to such a strict reference tone.

In addition, the shell tie test method is a test piece of silk with a drilled hole in the center 6Is of the length, as shown in Figure 1.
As shown in Figure 2, a stress was applied to the central part of the bend at three points, and the warping occurred during the night, resulting in a cracking rate of 5.
The apparent stress of 096 is measured and used as the sulfide cracking limit stress value (hereinafter referred to as Sc value). In Fig. 2, 2 is a glass round rod with a diameter of 4U, and 3 is a load Mr ( This is a bolt for adding stress).

In addition to improving these materials themselves, methods such as coating the steel material and injecting inhibitors into the corrosion zone have also been proposed, but none of these methods have been expected to produce sufficient results. .

The present inventors + Well, from the above-mentioned viewpoint, the Sc value is expressed by the formula,
S C≧(σy10-75))<l O-'kVk.

It has high strength with a yield strength of 65 to 9f/yit or more,
As a result of conducting research to obtain all button materials with sufficient performance as oil country tubular goods used in sour environments + b
・;To impart such properties to the material, (at t
The chemical composition of A is based on the entire composition of high-strength materials that can handle one current, and furthermore, within the range that can be mass-produced at present, S'i'l
He died with low mourning power for S of J, and what's more, he spent the remaining 8 minutes in Ca.
It is necessary to improve the cleanliness of the teeth by making the inclusions spheroidized during the treatment. It is also possible to become a fin, and therefore it is also 19 minutes Q, that there is a ulterior motive to reduce the force.

tel Furthermore, the uniform structure is ASTM &
Must have a grain hardening/tempering structure of 10 or more.

I have come to the knowledge as shown in (al~(ci) above, and have discarded it.

In addition, in order to reduce the austenite to a single grain of silica, it is necessary to heat the quenching step 11 rapidly and thoroughly.5 Furthermore, in order to obtain the desired crystal grains in thick-walled cypress products, it is necessary to quench the quenching process more than once35.
He also saw that it was necessary to repeat the process.

This invention was made based on the above findings, and includes C: 0.15-0.45% (hereinafter % is 1 weight 9°), St: 0.05-0.80'33 M
n: 0.30-1.709b, P: less than 0.008 dab, S2 0.003% or less, Cr: 0.20-1.
50%, Mo: Os05~0.809= , A
g: o, o 1-0.10 dabs Ca: Ca/S
The amount of N
b: 0°01~0.1υ%.

V: 0.01-0.109=, Cu: 0.10
-0.50%, W:0.20-1.00%.

Fe and unavoidable impurities: component ijk D
) - steel is subjected to Zl at least once to a temperature range of (Ac 3 points + 30C) and then quenched after being heated for a short time to improve the austenite grain size to ASTM A10.
By making the fc micrometer as described above and then tempering at a temperature below the Ac1 point, it has excellent 6i1 compound cracking resistance and yield strength: 65 to 9. f/nyr? It is characterized by the fact that the copper that is cooled above is manufactured in a similar manner.

Next, in this invention, the reason why each of the compositional amount of @, the heating rate of ; during quenching, and the total austenite grain size is limited as described above will be explained.

A Compositional component a) C The C component is an element that is effective in increasing the strength of steel during quenching and making it grainy, but if its content is less than 0.1590, the strength decreases and the outside of the quenching process occurs. oxidation, thus eliminating the need for tempering at low temperatures to achieve the desired strength.
25 repetitions of rapid heating and quenching for all five senses.A S
1ivi It became difficult to obtain a grain structure of A10 or higher, and the susceptibility to sulfide cracking became poor, while sail 4596
If it is contained in excess of
It was set as 5 to 0.4596.

b) 5i Sl is an effective element for removing C' from fill, and also has the effect of increasing strength and hardenability.
If the content is less than 0005 da δ, the desired effect cannot be obtained in the above-mentioned action, while if the content exceeds 0.80%, the susceptibility to sulfide cracking increases and the toughness deteriorates significantly. Therefore, the content should be set at 0.05 to 0.
It was set at 80%.

c) The IVln Mn component has the effect of increasing the quenching fi: and improving the overall toughness and toughness, but when the -f content is 0°3
If it is less than 0%, the desired effect will not be obtained, while if it exceeds 1.70%, segregation bands will be formed, resulting in deterioration of toughness, increased susceptibility to sulfide cracking, and susceptibility to quenching cracking. Therefore, the total amount of its content was determined to be 0.30 to 1.70%.

d) P P is one of the impurities that are inevitably brought into the tri process, but when its content exceeds 0.008%, it tends to segregate into a segregation layer, causing the structure of the steel to become non-uniform. Since C oxide increases the susceptibility to cracking, the total content is determined to be less than 0.008%.

e) SS is also an impurity that is inevitably introduced into steel, and it is desirable to reduce it as much as possible in order to improve toughness and sulfide cracking resistance. The upper limit of its content was set at 0.003% in consideration of all properties.

f) Cr The Cr component not only improves corrosion resistance.

Although it has the effect of increasing the hardenability and the hardening resistance, if its content is less than 0-, '209b, it is not possible to wait for the corresponding effect (1.501).
If the temperature exceeds 6 to 1, it becomes difficult to uniformly infiltrate the austenite during steep heating, and this also causes deterioration of toughness and increased susceptibility to quench cracking. ] i and ■ were determined to be 0.2 U to 1°509b.

g) Ai.

The Mo component increases the quenching depth and strength of EL'14, and increases the hardness and strength of EL'14, as well as increasing the hardening resistance.

It has the effect of improving toughness, but its content is 0005
? In the a-hemolyte groove, the desired effect cannot be obtained in the above-mentioned action, and on the other hand, even if the content exceeds 0.80%.

Not only will you not be able to obtain any further improvement effects.

However, since uniform hardening into austenite becomes difficult during rapid heating, its content [t k O, (15
~0°809a.

h) A/J Al component is added to stabilize the removal of CW9 from steel, but if its content is less than 0.0196, its effect is small; Even if the content exceeds O-01 to 0.b, the deoxidizing effect will not be improved any further, and furthermore, inclusions will cause scratches and deterioration of toughness. 1096.

i) Ca The Ca component has the effect of making all inclusions in the steel spherical, cleaning the steel, and reducing susceptibility to sulfide cracking.
The optimum amount of addition is closely related to the amount of S, and the amount of Ca
/S ratio must be in the range of 1 to 10. This is because when the Ca/S ratio is less than 1, stoichiometrically the inclusions are insufficiently spheroidized, whereas when the Ca/S ratio exceeds lO gold, nonmetallic inclusions such as Ca oxides are formed. Increasing,
This is because the cleanliness of ₛ・C deteriorates.

j) Nb and V Both Nb and V components contain fine austenite grains.
[(Since it has the effect of increasing the tempering softening resistance, it is included as necessary especially in the case of custom-made improvements, but if the content is less than 0.01%, the above-mentioned It is not possible to achieve the desired effect on the action, and on the other hand, if the content exceeds 0.10%, it will cause toughness deterioration, so each content ij) 0.0%
It was set at 1-0-10'%.

k) Cu The Cu component has the effect of suppressing the hydrogen absorption of copper and improving the sulfide cracking resistance, so it may be included as necessary when it is desired to further improve the sulfide cracking resistance. If the enrichment amount is less than 0.10%, the desired effects of 7Jr cannot be achieved.

On the other hand, if the content exceeds 005096, hot workability deteriorates, so the total i0. lO~0
It was set as 50%.

1) W The W component has tempering softening resistance '(il-) as it increases.

Since it has the effect of improving corrosion resistance, it is included as necessary when it is desired to further improve these characteristic sounds, but if the amount of O0 is less than 20%, the desired effect will not be achieved. 7'L, while 1. Even if the content exceeds 000qb, no further improvement effect is observed, and it is difficult to uniformly distribute the content into the austenite during rapid heating, so the content of It was set as .00%.

B. Heating temperature: If the heating temperature is less than (Ac3 point + 30℃J), the rapid short-time heating method as in the method of this invention will not convert the material into steel.
'<k uniform − Since it is difficult to completely austenite, heating ηAj transformation during quenching (Ac3 points +
30℃ or higher.

As a method for rapid heating, an induction heating method, a direct current heating method, or the like can be employed, but it is common to use a high frequency induction heating method. In this case, thin-walled products can be heated quickly using a high circumferential V number, but thick-walled products have a lower heating rate and a steeper temperature gradient, so it is necessary to lower the frequency by one frequency. will inevitably become lower. In any case, 1 copy 7'K 1~b <jj・'lAlthough it varies depending on the component, 1~30C
In the case of a relatively slow temperature increase rate of /see, it is desirable to repeat the quenching twice or more times.

C, Austenite grain size Austenite grain size is less than ASTM A 10'
At $4 coarse grains, the sulfide cracking resistance of high-strength materials becomes extremely low.
+f: &kkun, the particle size is determined by ASTM
It is set as 10 or more sake cups.

That is, FIG. 3 shows the chemical composition kl''r used in the present invention.
qfruS(J, 25%C-0,29%Si-0,4
8%Mn-0,006%P-0.002%S-0.00
72%Ca-0,78%Cr-0,37riJ'lo
-0,023%Nb-0,049%Al steel (Ca/S ratio: 3.6, Ac1 point: 755 C, ACII point: 8
60C), quenching conditions (heating speed, number of heating times, austenitizing temperature), and tempering temperature were changed to 2/l in total! This chart shows that the corrosion performance was adjusted using the shell tie test method, and the particle size and strength were adjusted by using two irons.
It is clear that a good Sc value can be achieved with the above grain layer.

Thus, the method of the present invention limits P and 8 minutes to less than 1,008% and 0°'J 03 Ii!b, respectively, and the Ca/S ratio is in the range 1-10 Enter -1.After making a bath of clean, uniform, and predetermined components of Ca-treated copper.

Add the elm to a saucepan, steel pipe, etc. using the usual method.

This is heated to a temperature of [Acg point +30°C] or higher using a rapid short-time heating method such as an Il-induction heating method or a direct current heating method, so that the entire structure is completely austenitized.

The quenching treatment with a suitable cooling medium is repeated at least once to uniformly bathe one alloying element Gk austenite, and the austenite grain size is adjusted to ASTM.
It is made to have an ultra-fine grain structure with an Ifx of 10 or more, and then sufficiently tempered to sufficiently temper the martensite produced by quenching to give it sulfide resistance. In other words, by tempering to a temperature below the Ac1 point, a steel k, nlQ is produced that has a strength of 7'f/mm' or more and excellent sulfide cracking resistance, making it suitable for each application. The tempering treatment removes the internal stress of the martensite generated by quenching and spheroidizes the cementite, giving the steel the desired performance.

As mentioned above, the present invention is characterized by a Ca-treated, low-S, low-P 11, clean and uniform material, and an ASTM 11
Combined with granulation, the yield strength is 65 K9f/1pt
n? This invention is said to have the above-mentioned strength, and was made based on the fact that it is possible to equip steel with 41 compound cracking resistance.Hereinafter, this invention will be explained in detail with reference to examples and comparisons with comparative examples. I will further explain to Hyotaichi.

Fruit L111 First, by the usual method, prepare the ingredients d as shown in Table 1.
Run's (: Tsukasa A-P made in Zenichi. Copper A-H.

It has the composition specified in Part 1 of this invention.

Pots ① to ① in Table 1 are marked with blanks and have compositions that are outside of the scope of the present invention in this respect.

Then, quenching was performed under the conditions shown in Table 2, and tempering was performed at a temperature of -25C at the Ac+ point.

The austenite grain size 1f (ASTM A), strength, and corrosion resistance of the six treated syllables were measured, and the results are also shown in Table 2.

Regarding the 1ljt eating ability, a test piece as shown in FIG. 1 was cut out from 6 steel, and the test piece was supported with a test piece support as shown in FIG. 5
% CH,5COOH+2200~3200 ppm
R+S.

Warm garden: 20°C 5 immersion time: 20 days The Sc value was added to the gold side in the test, and the value is shown. and.

The * mark in Table 2 indicates conditions that deviate from the conditions of the present invention.

From the results shown in Table 2, test numbers 1 to 8, in which the steel composition and heat treatment conditions are within the scope of the present invention, are AS
TM A of 10 or higher produces ultra-K (II-grained austenite crystal grains) and has extremely good strength and sulfide cracking resistance, but the composition, S temperature during quenching, and heating means are It is clear that in test numbers 9 to 23, which are outside the scope of the present invention, the bamboo compound cracking resistance is significantly inferior, even though there is not that much difference in strength.

Furthermore, from Table 2, even if the heating rate is relatively low as in test number 21, if the heating rate is about 2°QC/sec, two heat treatments are required as shown in test number 4. It is obvious that the desired customization can be achieved by doing this.

As mentioned above, according to the present invention, the yield strength is increased from 65 to 7.
f/mn? This ax has an extremely high strength as described above, and also has excellent corrosion resistance.
Relatively simple and easy to manufacture.

Major problems in developing oil or gas fields in sour environments
i'+'+Nevertheless, industrially useful effects are brought about, such as making it possible to make a significant contribution to energy resource development and the like.

[Brief explanation of the drawing]

Figure 1 (ii) shows an example of the L type corrosion resistance test piece. Figures 4 and 3 are schematic diagrams showing the state of the A S TM' material which has undergone heat treatment to adjust the grain size and strength in accordance with the present invention.
A chart showing the relationship between A and the yield strength and Sc value is shown below. In the drawings: 1. Test piece, 2. Glass round bar, 3. Stress-applied bolt. Applicant: Sumitomo Metal Industries Co., Ltd. Agent: Tomi 1) Kazuo, and 1 other person) Ichiri Tsuji (CL) (1))
≠Figure 2

Claims (1)

[Claims] ilI C: 0.15 to 0.45%. Si: 0.05-0.80 e! θ, Mn: 0
．． 30-1.70%, P: less than 0°0OE1. S20. QQ396 or less. Cr: 0-20~]-50q6. Mo: 0.05~. 0.80%, Ad: 0.01-0.10%. Ca: Contains total amount of 1 to 1O in Ca/S ratio. Fe and unavoidable impurities: remaining, to the steel with the composition (or more positive %) consisting of CAca
Point +3 (I) The austenite grain size is refined to ASTM version 10 or higher by applying the treatment of rapid short-time heating to a temperature range of CJ or higher and then quenching at least once, and then AC
It is characterized by tempering to a temperature of 1 point or less. 1l
jjMethod for producing ρj-strength copper having excellent f' sulfide cracking properties. (21C: 0015-0.45 squirrel. Si: 0°05-0.809b. Mn: 0-30-1-70%. P: less than 0.008%, S: 0-0039b or less, Cr: 0. 20-1.50 Da6, MO: o.05-0.80%. Aa: o.01-o, 1oL3b. Ca: Contains an amount of 1-10 in Ca/S ratio, and further contains Nb : o, oi~0°10%, V: O, O1~0.10 dab. Cu: 0-10~0-509o. W: 0.20~1.ooqb. 4?] fc
, (C3 point A A method for producing high-strength steel endowed with good sulfide crackability, characterized by tempering.